Combustor liner cap assembly

BACKGROUND

This disclosure relates generally to a gas turbine engine and more particularly to a liner cap assembly for a gas turbine engine combustor.

Gas turbine engines, preferably of an industrial type, use one or more combustors that burn fuel to rotationally drive a turbine section of the engine. Some combustors include a liner cap assembly at a leading end of the combustor. The liner cap assembly supports fuel injection components, for example.

Many gas turbine engines include a dry low NOx (DLN) system for reducing emissions. Some DLN systems premix the fuel and air prior to their injection as a mixture into the combustion chamber. The DLN systems can create pressure pulsations during combustion that subjects the liner cap assembly to vibratory deformations that are detrimental to component fatigue life and can cause premature failure of the entire combustion system. This effect may be exacerbated if the vibratory frequencies are close to the natural frequency of the liner cap assembly thus shortening part life. To this end, it is desirable to stiffen the liner cap assembly both to strengthen it and to raise its natural frequency above the likely frequencies of the DLN pressure pulsations.

SUMMARY

A liner cap assembly is disclosed for use in a gas turbine engine combustor. The assembly includes an outer ring that extends along an axis. Multiple struts are arranged circumferentially about an inner diameter of the outer ring and extend radially inwardly therefrom. An inner ring and a plate are supported by the struts. The plate is arranged with the inner ring so that it is aligned axially with the struts. The plate includes multiple circumferential openings that support a collar and a premix tube at each of the openings. The plate is arranged between leading and trailing edges of the struts to provide a stiffened liner cap assembly that is robust and resistant to the vibrations typically found in dry low NOx systems.

Other advantages of the disclosure can be understood by reference to the following detailed description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idrefs="DRAWINGS">FIG. 1</figref> is a cross-sectional view of a combustor for an industrial gas turbine engine, including a liner cap assembly;

<figref idrefs="DRAWINGS">FIG. 2</figref> is an end view of the liner cap assembly shown in <figref idrefs="DRAWINGS">FIG. 1</figref>; and

<figref idrefs="DRAWINGS">FIG. 3</figref> is a cross-sectional view of the liner cap assembly taken along line <b>3</b>-<b>3</b> in <figref idrefs="DRAWINGS">FIG. 2</figref>.

DETAILED DESCRIPTION

An industrial gas turbine engine <b>10</b> is schematically shown in <figref idrefs="DRAWINGS">FIG. 1</figref>. The engine <b>10</b> includes one or more combustors <b>12</b> (only one shown) arranged between compressor and turbine sections <b>14</b>, <b>16</b>. The combustor <b>12</b> is secured to structure <b>11</b> of the engine <b>10</b>. The combustor <b>12</b> receives air A from the compressor section <b>14</b>. The air is mixed with fuel and ignited, as is known, to rotationally drive the turbine section <b>16</b>.

The combustor <b>12</b> includes a combustor housing <b>18</b> that is secured to the structure <b>11</b>. The combustor housing <b>18</b> includes an outer sleeve <b>20</b> that is arranged about a liner <b>22</b> that provides the combustion chamber, providing an annular passage <b>24</b>. The outer sleeve <b>20</b> includes multiple holes <b>28</b> that permit the air A to enter the annular passage <b>24</b>.

A liner cap assembly <b>30</b> is received by the outer sleeve <b>20</b> and secured to the combustor housing <b>18</b>. The liner cap assembly <b>30</b> receives multiple fuel injectors <b>32</b>, in one example, five injectors. The fuel injectors <b>32</b> deliver fuel to premix tubes <b>42</b> and then to the combustion chamber, where it is ignited by an igniter <b>34</b>. The combusted mixture is delivered through a transition duct <b>26</b> to the turbine section <b>16</b> where it is expanded to rotationally drive the turbine section <b>16</b>. A cover <b>36</b> is arranged over a forward end of the combustor housing <b>18</b> to support the fuel injectors <b>32</b>.

The liner cap assembly <b>30</b> includes multiple collars <b>38</b>, which receive the fuel injectors <b>32</b>. A swirler <b>40</b> is arranged within each collar <b>38</b> about its respective fuel injector <b>32</b>, in one example. The swirler <b>40</b> swirls the air A as it enters each passageway provided by its respective collar <b>38</b>, which are generally cylindrical in shape. The collars <b>38</b> are mounted to a plate <b>46</b> that supports generally cylindrical premix tubes <b>42</b> that are arranged coaxially with their respective collar <b>38</b>. The swirler <b>40</b> and premix tubes <b>42</b> of the liner cap assembly <b>30</b> provide swirling fuel-air mixtures to the combustion chamber <b>20</b> where they are burned. However, such dry low NOx systems can subject the liner cap assembly <b>30</b> to detrimental vibrations. To this end, it is desirable to provide a robust liner cap assembly <b>30</b> with resonant frequencies high enough that the resonance will not be excited by the DLN pressure pulsations.

Referring to <figref idrefs="DRAWINGS">FIGS. 2 and 3</figref>, the liner cap assembly <b>30</b> includes leading and trailing ends <b>48</b>, <b>50</b> through which the air A respectively enters and exits. An outer ring <b>52</b> of the liner cap assembly <b>30</b> includes a flange <b>54</b> that is used to secure the liner cap assembly <b>30</b> to the combustor housing <b>18</b>. Multiple struts <b>44</b> are arranged circumferentially about the outer ring <b>52</b> and are secured at its inner diameter. In one example, the struts <b>44</b> are generally trapezoidal in shape. The plate <b>46</b> is axially aligned with the struts <b>44</b> and secured axially relative to an axis X between their leading and trailing edges <b>80</b>, <b>82</b>. An inner ring <b>56</b> is secured to the plate <b>46</b>, for example, by welding. The struts <b>44</b> are secured to the inner ring <b>56</b>, for example, by welding. The plate <b>46</b> is perpendicular to the wall of both the inner ring <b>56</b> and the outer ring <b>52</b> with struts <b>44</b> between them. This arrangement results in a very stiff structure that allows the combustor housing <b>18</b> and structure <b>11</b> to resist the pressure pulsation induced vibrations of the liner cap assembly <b>30</b>. With the plate <b>46</b> in the example position shown, the liner cap assembly <b>30</b> is capable of withstanding significant pressure pulsations during combustion in dry low NOx systems.

The plate <b>46</b> includes circumferentially arranged openings <b>66</b>. One side of the plate <b>46</b> includes an annular recess <b>60</b> about each opening <b>66</b> that receives an outwardly extending radial lip <b>62</b> at one end of the collar <b>38</b>. Tabs <b>68</b> are arranged over the radial lip <b>62</b> and secured to the plate <b>46</b>, for example, by welding, to retain the collar <b>38</b> relative thereto. The collar <b>38</b> extends from the radial lip <b>62</b> to an end <b>64</b> that receives the fuel injector <b>32</b> and swirler <b>40</b>.

The inner ring <b>56</b> is arranged within the outer ring <b>52</b> and is coaxial with it about an axis X. In one example, the inner ring <b>56</b> extends from and is supported by the plate <b>46</b> on a side opposite the side that supports the collars <b>38</b>. The premix tubes <b>42</b> are aligned with their respective openings <b>66</b> and arranged radially inwardly of the inner ring <b>56</b>. The premix tubes <b>42</b> extend axially from the plate <b>46</b> to a rear plate <b>70</b>. Further, the inner ring <b>56</b> may include cooling holes <b>58</b> allowing compressor air to flow into the liner cap assembly <b>30</b>.

An impingement plate subassembly <b>72</b> is secured to the inner ring <b>56</b> by fasteners <b>74</b>. A spring <b>76</b> is supported on an outer surface of the impingement plate subassembly <b>72</b>. The spring <b>76</b> is received by the outer sleeve <b>20</b> (<figref idrefs="DRAWINGS">FIG. 1</figref>) to secure it to the liner cap assembly <b>30</b>.

Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.